I have a spa that calls for a 50amp gfci in a outdoor box. This box and wir ing was there before I moved in . But in the main box in the house there is a 20amp breaker 2pole in a sub panel. Do I need a 50 amp 2pole to match the gfci thats in the outdoor squareD box.

Yes, the breaker needs to a 50. The wire size will have to be increased if not appropriate for 50 amp. Check with the dealer you just bought your spa from. They should be more than helpful. Not a bad idea to get an electrician involved and/or your town's electrical inspector from the building department.

I got 6 gauge for red and black hot. Neutral 6,negative 8. Its about 80 ft to the outside box. I will call an electrical inspector. That should be the correct gauge wire. What do you think.

It sounds right. Your town's electrical inspector should be happy to come out and check the existing wiring. He/ she probably won't require a permit since it's an existing installation. Best to get their o.k.

6 ga wire is exactly what you need. I am in process of getting mine wired right now.